A thermal evaporation device with controllable evaporation rate for evaporating bismuth telluride film

Abstract

The present invention belongs to the field of vacuum evaporation technology and relates to a thermal evaporation device for evaporating bismuth telluride films with a controllable evaporation rate. The device comprises a evaporation body made of a conductive material, an evaporation source, and electrodes located at both ends of the evaporation body. The evaporation body defines a chamber, the evaporation source is fixed at one or both ends of the chamber, and a plurality of circular holes are provided at the end of the evaporation body away from the evaporation source or in the middle of the evaporation body. The evaporation body is made of a seamless tube made of a nickel-chromium alloy, and the electrodes are formed by integrally forming the ends of the seamless tube by shrinking and flattening. The thermal evaporation device of the present invention has a controllable evaporation rate. Its integrally formed electrode structure, flexible circular hole layout, specific evaporation source preparation process, and optimized evaporation body structure are particularly suitable for preparing high-precision, high-quality bismuth telluride films. The device's technical specifications reach internationally leading levels, providing a disruptive technology platform for the industrialization of next-generation high-performance thermoelectric devices.

Description

Technical Field

[0001] The present invention belongs to the field of vacuum evaporation technology and relates to a thermal evaporation device with a controllable evaporation rate for evaporating bismuth telluride films. The thermal evaporation device can realize the preparation of high-quality Bi2Te3 thermoelectric thin film devices, effectively control the evaporation rate of the evaporation source, and effectively improve the performance of the thermoelectric thin film devices. Background Art

[0002] Thermoelectric materials are solid materials that can convert heat energy into electrical energy. Bismuth telluride (Bi2Te3) is widely used in thermoelectric materials, electronic components and other fields due to its excellent thermoelectric properties. It is also a thermoelectric material that has been studied earlier and has relatively mature technology. Most thermoelectric cooling components currently use this type of material. To achieve these applications, it is usually necessary to deposit it on a substrate through a coating technology to form a thin film. Existing bismuth telluride thin films are mostly prepared by magnetron sputtering. From a thermodynamic perspective, the growth mode of thin films prepared by magnetron sputtering is a three-dimensional island growth mode. This growth mode is prone to forming internal stress during the film formation process, resulting in high internal stress in the product film. Even with subsequent annealing processes, it is difficult to completely eliminate this internal stress. The presence of this internal stress will continue to affect the thermoelectric properties of the film, thereby affecting the use of thermoelectric devices in thin film applications.

[0003] Thermal evaporation, a key branch of physical vapor deposition (PVD), has been widely used in optical coatings, semiconductor devices, solar cells, and other fields. Its principle is to evaporate or sublimate the film-forming material in a vacuum environment through methods such as resistance heating or electron beam bombardment. After a period of transport, the material condenses or deposits on the surface of a low-temperature workpiece or substrate to form a coating. Based on the type of heating source, thermal evaporation can be categorized as: resistance heating evaporation, which uses high-temperature resistant metals such as tungsten and molybdenum as a heating element for direct or indirect heating and evaporation; electron beam evaporation, which focuses a high-energy electron beam to heat the material; and laser evaporation, which achieves localized evaporation through instantaneous heating of the material using laser pulses. Thermal evaporation technology can produce high-purity thin films while effectively preventing impurity incorporation. It also allows for precise control of composition and thickness. The deposition rate can be precisely controlled by simply adjusting the evaporation source temperature (or current intensity) and the deposition time. However, thermal evaporation also has certain drawbacks, such as a short evaporation source life. Traditional resistive-heated evaporation sources (such as tungsten filaments and molybdenum boats) are prone to reacting with the evaporation material at high temperatures. At high temperatures, some evaporation material atoms diffuse into the tungsten filament lattice, forming brittle compounds and causing the evaporation source to break and fail. For example, when a quartz crucible is used to hold the material, the quartz reacts with the bismuth telluride at high temperatures during external resistance heating, leading to film contamination. Material utilization is low. The point-source nature of thermal evaporation results in a hemispherical evaporation distribution, with only approximately 10-15% of the material deposited on the substrate, while the remaining 85-90% is wasted on the vacuum chamber walls and baffles, significantly increasing production costs. Dual-source evaporation, which separates Bi and Te and uses a mass flowmeter to control the ratio of Bi and Te to form bismuth telluride on the substrate surface, requires precise synchronization of the evaporation rates of the two materials, resulting in complex and costly equipment. Furthermore, ion-beam-assisted deposition, which uses ion beam bombardment to improve film density, increases the risk of substrate damage and requires more complex and expensive equipment.

[0004] In traditional evaporation processes, heating is often performed using point source heating, line source heating, or a combination of the two. However, as the size of the evaporation substrate increases, traditional heating methods cannot meet the requirements of large-area uniformity, and the evaporation rate is difficult to accurately control. Commonly used devices for thermal evaporation are evaporation crucibles or evaporation boats, in which the vaporization and evaporation rate of the evaporation material is proportional to the heating temperature inside the evaporation crucible. The higher the heating temperature inside the evaporation crucible, the faster the heat transfer rate, and the higher the vaporization and evaporation rate of the evaporation material. After the evaporation material inside the evaporation crucible begins to vaporize and evaporate, the solid state of the evaporation material gradually decreases, causing the internal space of the evaporation crucible to increase. The vapor pressure inside the evaporation crucible decreases as the diffusion space inside the evaporation crucible increases, thereby reducing the vaporization and evaporation rate of the evaporation material. In order to maintain a constant vaporization and evaporation rate of the evaporation material, it is necessary to continuously increase the heating temperature inside the evaporation crucible as the evaporation time of the evaporation material increases. To this end, some people use a tungsten wire winding method, winding a tellurium-bismuth alloy around the surface of a tungsten wire and heating it with electricity to evaporate it. However, this method is susceptible to material shedding at high temperatures due to the difference in thermal expansion coefficients between the evaporating material and the tungsten filament. Local overheating of the tungsten filament can easily cause it to burn out. Furthermore, the tellurium-bismuth alloy is prone to splashing or dripping from the evaporation source surface at high temperatures, affecting film uniformity and thickness control, leading to reduced film quality. Other methods use evaporation boats stamped from nickel-based alloy strips. However, these boats suffer from cracking at the edges, leading to vapor escape (the cracking rate is >30% for thicknesses ≤0.1 mm). The evaporation rate also fluctuates widely, making it impossible to control vapor directionality. Furthermore, increasing the required heating temperature increases energy consumption and costs, while also potentially overheating the evaporation source, causing raw material decomposition and preventing the production of thermally evaporated material. Film quality is directly related to the temperature and rate of evaporation. To obtain a uniform film layer, the evaporation material needs to be heated evenly. For this purpose, there have been many studies on heat sources or evaporation devices, hoping to improve the heating uniformity of the evaporation heating system. For example, CN222139240U discloses an evaporation heating and cooling system and evaporation equipment, including: a cooling device, a heating device, an evaporation material container and a temperature control device. The heating device is arranged in the cooling device, and the heating device includes a heating component and a heat-conducting medium container. The evaporation material container is arranged in the heat-conducting medium container, and the heat-conducting medium container is used to transfer heat to the evaporation material container. Since the evaporation material container is placed in the heat-conducting medium container, the heat-conducting medium container can transfer heat from the bottom and side to the evaporation material container, and the temperature control device can control the heat distribution in the heat-conducting medium container to be uniform, so that the evaporation material container can be ensured to be heated more evenly, which is conducive to quickly and accurately controlling the heating rate of the evaporation material, thereby improving the coating quality and coating efficiency.CN118773551A discloses an evaporation source and an evaporation device, wherein the evaporation source includes a crucible, an electromagnetic coil, a support structure, and an inductor; the crucible is used to load the evaporation material; the electromagnetic coil is arranged around the crucible, and the electromagnetic coil is used to generate an electromagnetic field under the control of an alternating current; the support structure is located in the crucible and is fixedly connected to the crucible; the inductor is located on the support structure, and the inductor is used to generate an induced current under the action of the electromagnetic field to heat the evaporation material in the crucible, thereby directly heating the evaporation material from the inside of the crucible. The thermal interaction is simple and efficient, the heating efficiency is improved, the hysteresis of the temperature control is improved, and the process stability of the evaporation can be significantly improved, and the product performance and production yield can be improved. CN110777334B discloses an evaporation source and a vacuum evaporation system, wherein the evaporation source includes: a cavity, a crucible and a driving assembly arranged in the cavity, and a heating assembly; wherein the crucible is a retractable structure for placing the evaporation material; an air outlet is provided on one side of the cavity, the driving assembly is located on the side of the crucible away from the air outlet, and the driving assembly is used to drive the crucible to shrink toward the side close to the air outlet; and the heating assembly is used to heat the evaporation material. Since the crucible in the present application is a retractable structure, the driving assembly can drive the crucible to shrink toward the side close to the air outlet. Therefore, in the process of gradually reducing the evaporation material in the crucible, the distance between the evaporation material and the air outlet can always be maintained within a small range, and the deposition rate of the evaporation material can be ensured to remain stable without increasing the heating temperature, thereby avoiding the influence of excessive temperature on the quality of the film layer formed on the substrate. CN110629168B discloses an evaporation device of a vacuum coating machine, comprising: an evaporation boat, a heating system, and an air distribution system. The evaporation boat comprises an inner layer, an outer layer, and a movable cover. The inner layer is located between the outer layer and the movable cover. The movable cover is provided with a plurality of evaporation holes. The inner layer of the evaporation boat is provided with evaporation grooves corresponding to the evaporation holes. The heating system comprises a plurality of relatively independent evaporation sources. The evaporation source is provided with an inner crucible, which is nested in the evaporation groove. The evaporation source can heat an object placed in the inner crucible. A multi-stage binary air distribution pipeline is provided to achieve uniform control of the air intake amount, so that the evaporated gas and the external gas can be fully mixed to form a uniform composite film. CN105603364B discloses a heat-conducting device and an evaporation crucible. The heat-conducting device includes a heat-conducting tube and a plurality of heat-conducting plates mounted on the heat-conducting tube in a radial shape, or includes a radial heat-conducting tube in a radial shape. By placing the above-mentioned heat-conducting device in the evaporation crucible, the heat on the crucible wall can be evenly transferred to the interior and center of the crucible through the heat transfer path of the heat-conducting device, which is beneficial to improving the uniformity of heating of the material inside the crucible, so that the evaporation state of the material remains stable, and the evaporation effect is improved. In addition, the heat-conducting device is easy to process, low in cost, and has good thermal conductivity.CN106987807B discloses an evaporation source, an evaporation device, and an evaporation method, comprising: an evaporation crucible; a movable platform disposed within the evaporation crucible, the movable platform comprising at least a bottom plate for placing the evaporation material, the movable platform surrounding the sides and top surface of the evaporation crucible to form an evaporation cavity; and a moving mechanism for driving the movable platform to move within the evaporation crucible in a direction perpendicular to the bottom plate. This method solves the problem in existing evaporation crucibles where vaporization and evaporation of the evaporation material increases the internal diffusion space, thereby reducing the evaporation rate and affecting the evaporation effect. CN220012776U discloses an evaporation boat and an evaporation device, which includes a boat body and an electrode connection structure located at opposite ends of the boat body along a first direction. The boat body extends along the first direction, and at least one row of evaporation grooves is provided on the first surface of the boat body. The evaporation grooves are used to place evaporation materials. After the evaporation materials are added to each evaporation groove, the materials in each evaporation groove of the boat body are uniform, the temperatures in each evaporation groove of the boat body are uniform, and the evaporation rates in each evaporation groove of the boat body are similar, thereby achieving the purpose of improving the uniformity of vacuum coating and improving the quality of vacuum coating. CN107400859A discloses an evaporation source, comprising an evaporation source body made of a conductive material. The evaporation source body comprises a main body, within which a material chamber is defined. A first electrode connection terminal and a second electrode connection terminal having a polarity opposite to that of the first electrode connection terminal are provided at any position outside the main body. When the first electrode connection terminal and the second electrode connection terminal are energized, the main body itself conducts electricity to generate heat to heat the material within the material chamber. Compared to existing evaporation sources, the evaporation source provided by the present invention is itself made of a conductive material. By providing positive and negative electrodes at corresponding positions of the evaporation source, self-heating of the evaporation source can be achieved, thereby obtaining a uniform heating effect and producing a high-quality film layer by evaporation deposition.

[0005] However, most current thermal evaporation devices still require vacuum or negative pressure environments. These complex devices lack versatility, and the inability to effectively control the target evaporation rate results in poor uniformity in the bismuth telluride film, hindering the performance of the resulting thin film. This severely impacts the quality and production efficiency of tellurium-bismuth alloy thin films. Therefore, it is necessary to provide a thermal evaporation device with a controllable evaporation rate to overcome these challenges and produce high-performance bismuth telluride thin films. Summary of the Invention

[0006] In order to solve the defects in the prior art, one object of the present invention is to provide a thermal evaporation device with a controllable evaporation rate for evaporating bismuth telluride film, the evaporation device including an evaporation body made of a conductive material, an evaporation source and electrodes located at both ends of the evaporation body, a chamber is opened inside the evaporation body, the evaporation body and the electrode are integrally formed, the evaporation source is 1 or 2, when the evaporation source is 1, the evaporation source is fixed at one end of the chamber, and a plurality of circular holes are provided on the surface of the end of the evaporation body away from the evaporation source; when the evaporation source is 2, a plurality of circular holes are provided on the middle surface of the evaporation body, and the evaporation sources are symmetrically fixed at the ends of the circular holes away from the chamber. The integrated formation of the evaporation body and the electrode reduces assembly steps, reduces operation difficulty and maintenance costs, improves the overall stability and reliability of the equipment, reduces the problem of increased resistance or unstable current caused by poor connection, and cooperates with the evaporation body of conductive material to effectively conduct current, ensure that heat is evenly distributed on the entire evaporation source, avoid local overheating, make the surface temperature of the entire evaporation source more uniform, reduce the risk of material sputtering and dripping, achieve a more stable heating effect, and improve current efficiency; according to the setting of the evaporation source, the corresponding end of the evaporation body away from the evaporation source or the middle area of ​​the evaporation body away from the evaporation source By setting up a number of circular holes, the evaporation rate can be precisely controlled. That is, the evaporation rate can be adjusted by adjusting the aperture size, number, and opening and closing state of these circular holes, so as to obtain a film of desired thickness and uniformity. The overall design of the thermal evaporation device helps to maintain an isolated internal environment. When the device is heated for use, the internal air is quickly expelled. As the evaporation source evaporates, the internal air is further discharged, making the evaporation process more efficient and less affected by external interference, ensuring the uniform volatilization of the bismuth telluride material during the evaporation process, thereby forming a film with consistent thickness and uniform composition, and realizing the preparation of bismuth telluride thermoelectric films by thermal evaporation without vacuum conditions.

[0007] Furthermore, the deposition body is made of a seamless nickel-chromium alloy tube, and the electrodes are formed by shrinking and flattening the ends of the seamless tube into an integral piece. Nickel-chromium alloy has excellent high-temperature resistance and mechanical strength, enabling stable operation in high-temperature environments for extended periods, avoiding the burnout problem often associated with traditional materials.

[0008] Furthermore, the distance between two adjacent circular holes on the evaporation body is equal. When there is one evaporation source, the circular holes are 2 to 10 and are evenly arranged at one end of the evaporation body. When there are 2, 3, 5 or 7 circular holes, the circular holes are arranged along the length of the seamless tube or the circumferential surface; when there are 4 or 10 circular holes, the circular holes are arranged in two rows along the length of the seamless tube; when there are 6 circular holes, the circular holes are arranged in two or three rows along the length of the seamless tube; when there are 8 circular holes, the circular holes are arranged in two or four rows along the length of the seamless tube; when there are 9 circular holes, the circular holes are arranged in three rows along the length of the seamless tube. When there are 2 evaporation sources, the circular holes are 2 to 10 and are evenly arranged in the middle of the evaporation body along the length or circumferential surface of the seamless tube. When the number of circular holes is 2, 3, 5 or 7, the circular holes are arranged along the circumferential surface of the seamless tube; when the number of circular holes is 4 or 10, the circular holes are arranged in two rows along the circumferential direction of the seamless tube; when the number of circular holes is 6, the circular holes are arranged in two or three rows along the circumferential direction of the seamless tube; when the number of circular holes is 8, the circular holes are arranged in two or four rows along the circumferential direction of the seamless tube; when the number of circular holes is 9, the circular holes are arranged in three rows along the circumferential direction of the seamless tube.

[0009] Furthermore, the circular holes have a diameter of 0.02-0.5 mm, and the distance between adjacent circular holes is 0.5-2 mm, more preferably 1 mm. The evenly distributed circular holes can effectively control the evaporation rate and vapor volume, helping to achieve uniform heating of the evaporation source, ensuring uniform thin film deposition and reducing sputtering.

[0010] It is further preferred that the circular holes have different diameters, with the small aperture being 0.02mm~0.1mm, which can suppress local overpressure, produce laminar flow effect, and reduce steam turbulence kinetic energy; the large aperture being 0.2mm~0.5mm can ensure the overall flow rate and achieve a stable evaporation rate; the large and small apertures in the circular holes can be adjusted according to the needs of coating speed, thickness, etc., and the device has strong versatility.

[0011] Furthermore, the chromium content in the nickel-chromium alloy is 20wt%~22wt%, the diameter of the seamless pipe is 25mm, the pipe wall thickness is 0.05~0.5mm, and the aspect ratio is 5:1~10:1.

[0012] Furthermore, the surface of the chamber of the evaporation body is coated with a Ti-Al2O3 coating with a thickness of 2 to 5 μm. This coating not only enhances the corrosion resistance and oxidation resistance of the chamber, but also increases the surface hardness, thereby extending the service life of the equipment.

[0013] Furthermore, the evaporation source is Bi2Te3-1wt%Te. The above setting can compensate for the preferential loss of Te during the evaporation process and maintain the stoichiometric ratio of the evaporated material.

[0014] Another object of the present invention is to provide a method for preparing a vapor deposition device for evaporating a bismuth telluride film, comprising the following steps:

[0015] 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum degree of 0.01Pa, and melt at 620℃ for 2h; maintain a solidification rate of 0.05K / s, cool to room temperature, and crush the product to 200 mesh before loading it into a mold. Isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm. Place it in a vacuum sintering furnace, raise the temperature to 450℃ at a rate of 5℃ / min, hold it for 2h, and then cool it to room temperature with the furnace. When the evaporation source is used for evaporation coating, after connecting the current to 3A~3.5A, the tellurium-bismuth alloy begins to evaporate from the small holes, forming a uniform thin film.

[0016] 2) Preparation of the evaporation body: Select a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1 to 10:1, and a thickness of 0.05 to 0.5 mm, deposit a Ti-Al2O3 coating with a thickness of 2 to 5 μm on the inside of the seamless tube, and use laser drilling to form 2 to 10 evenly distributed circular holes with a diameter of 0.02 to 0.5 mm at a distance of 20 mm from one end of the seamless tube; Alternatively, select a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1 to 10:1, and a thickness of 0.05 to 0.5 mm, deposit a Ti-Al2O3 coating with a thickness of 2 to 5 μm on the inside of the seamless tube, and use laser drilling to form 2 to 10 evenly distributed circular holes with a diameter of 0.02 to 0.5 mm on the surface of the seamless tube in the middle area of ​​the two evaporation sources;

[0017] 3) Using high-temperature ceramic adhesive, secure the evaporation source to the end of the chamber away from the circular hole. Curing was performed at 250°C for 30 minutes. The ends were then shrunk using a spinning machine and flattened to form an integrally formed electrode. The high-temperature ceramic adhesive was selected from Aremco Ceramabond 571 from Aremco Products, Inc.

[0018] Furthermore, there are 6 circular holes, which are distributed in two rows along the length direction of the seamless pipe, and the distance between two adjacent holes is 1 mm.

[0019] Furthermore, the compression amount of each pass during the necking is 3% to 5%; the flattening treatment is specifically carried out in two stages, first maintaining the pressure at 50 MPa for 20 seconds, and then impact loading 3 times at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] The thermal evaporation device provided by this invention solves problems such as material sputtering, short evaporation source life, and uncontrollable parameters in traditional evaporation processes. It also significantly improves film quality and device durability, and has broad application prospects. First, the evaporation body and electrodes are integrally formed, reducing assembly steps and improving the overall stability and reliability of the device. This also reduces contact resistance, improves current transmission efficiency, and enhances the overall mechanical strength and stability of the device. It also reduces the risk of damage due to vibration or impact, and avoids the burn-out problem that is common with traditional materials.

[0022] 2. Nickel-chromium alloy seamless pipes have excellent high temperature resistance and mechanical strength, and can work stably for a long time in high temperature environments. Combined with the setting of special surface coating, it not only enhances the corrosion resistance and oxidation resistance of the chamber, but also improves the surface hardness, extends the service life of the equipment, and improves the mechanical strength and electrical connection stability of the equipment.

[0023] 3. The evenly distributed circular holes and their corresponding arrangement with the evaporation source facilitate uniform heating and evaporation of the evaporation source, ensuring uniformity and consistency in thin film deposition and effectively controlling the evaporation rate and vapor volume. The evaporation source is prepared through vacuum melting and isostatic pressing, ensuring the purity and density of the raw materials, improving the quality of the final product and enhancing the performance of the material. This invention, through the trinity of innovation in materials, structure, and process, achieves a generational leap in performance in the field of thermoelectric thin film evaporation, bringing the equipment's technical specifications to internationally leading levels and providing a disruptive technology platform for the industrialization of next-generation high-performance thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic plan view of a thermal evaporation device prepared in Example 1 of the present invention;

[0025] Figure 2 A schematic plan view of a thermal evaporation device prepared in Example 2 of the present invention;

[0026] Figure 3 A schematic plan view of a thermal evaporation device prepared in Example 3 of the present invention;

[0027] Figure 4 This is a SEM morphology image of a Bi2Te3 thin film prepared by thermal evaporation in Example 3 of the present invention;

[0028] Figure 5 A schematic plan view of a thermal evaporation device prepared in Example 4 of the present invention;

[0029] Wherein: 1-electrode, 2-circular hole, 3-evaporation body, 4-bismuth telluride evaporation source, 5-substrate. DETAILED DESCRIPTION

[0030] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved more clearly, the technical solutions of the embodiments of the present invention will be further described in detail below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] It should be noted that references to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are commercially available unless otherwise specified.

[0033] Example 1

[0034] In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in two rows along the length direction of the seamless tube, and the circular holes have the same size. The schematic diagram of the device is shown in FIG. Figure 1 , the preparation method of the evaporation device is as follows:

[0035] 1) Preparation of the evaporation source: Weigh 4N purity Bi2Te3 powder and Te powder in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum of 0.01 Pa, and melt at 620°C for 2 hours. Maintain a solidification rate of 0.05 K / s, cool to room temperature, crush the product to 200 mesh, and then place it into a mold. Isostatically press at 200 MPa for 20 minutes to obtain a green body with a diameter of 24 mm and a thickness of 4 mm. Place the green body in a vacuum sintering furnace, increase the temperature to 450°C at a rate of 5°C / min, hold at this temperature for 2 hours, and then cool it to room temperature with the furnace.

[0036] 2) Preparation of the deposition body: A nickel-chromium alloy (chromium content 20 wt%) seamless tube with a diameter of 25 mm, an aspect ratio of 5:1, and a thickness of 0.05 mm was selected. A 2 μm thick Ti-Al2O3 coating was deposited on the inside of the seamless tube. Six evenly distributed circular holes with a diameter of 0.1 mm and a distance of 0.5 mm between adjacent holes were formed by laser drilling 20 mm from one end of the seamless tube.

[0037] 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at the end of the chamber away from the circular hole, so that the surface of the evaporation source is parallel to the length direction of the evaporation body. Curing at 250°C for 30 minutes, and using a spinning machine to shrink the ends, with a compression amount of 3% per pass. The ends after shrinking are flattened to form electrodes. The flattening is carried out in two stages: first, maintaining the pressure at 50 MPa for 20 seconds, and then impact loading at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz for three times.

[0038] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.2°C. The evaporation film formation rate was relatively stable. The film thickness uniformity deviation was measured to be ≤1.3%, and the product composition was stable. After continuous coating of 200 pieces, the evaporation device was still able to work stably.

[0039] Example 2

[0040] In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in three rows along the length direction of the seamless tube, and the circular holes have different sizes. The schematic diagram of the device is shown in FIG. Figure 2 , wherein the diameter of the large circular hole is 0.5 mm and the diameter of the small circular hole is 0.02 mm. The preparation method of the evaporation device is as follows:

[0041] 1) Preparation of the evaporation source: Weigh 4N purity Bi2Te3 powder and Te powder in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum of 0.01 Pa, and melt at 620°C for 2 hours. Maintain a solidification rate of 0.05 K / s, cool to room temperature, crush the product to 200 mesh, and then place it into a mold. Isostatically press at 200 MPa for 20 minutes to obtain a green body with a diameter of 24 mm and a thickness of 4 mm. Place the green body in a vacuum sintering furnace, increase the temperature to 450°C at a rate of 5°C / min, hold at this temperature for 2 hours, and then cool it to room temperature with the furnace.

[0042] 2) Preparation of the deposition body: A nickel-chromium alloy (chromium content 22 wt%) seamless tube with a diameter of 25 mm, an aspect ratio of 10:1, and a thickness of 0.5 mm was selected. A 5 μm thick Ti-Al2O3 coating was deposited on the inside of the seamless tube. Six circular holes were formed by laser drilling 20 mm from one end of the seamless tube, with a distance of 1 mm between adjacent holes.

[0043] 3) Using Aremco Ceramabond 571, secure the prepared evaporation source to the end of the chamber away from the circular hole, with the surface of the evaporation source perpendicular to the length of the evaporation body. Curing was performed at 250°C for 30 minutes. The ends were then shrunk using a spinning press, with each pass applying 5% compression. The shrunk ends were then flattened to form electrodes. This flattening was performed in two stages: first, maintaining a pressure of 50 MPa for 20 seconds, followed by three impulse loads at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz.

[0044] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.5℃. The evaporation film formation rate was relatively stable, and the film thickness uniformity deviation was measured to be ≤1%. The product was relatively stable, and the evaporation device was still able to work stably after continuously coating 500 pieces.

[0045] Example 3

[0046] In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in three rows along the length direction of the seamless tube. The circular holes have the same size and diameter of 0.5 mm. The schematic diagram of the device is shown in FIG. Figure 3 , the preparation method of the evaporation device is as follows:

[0047] 1) Preparation of the evaporation source: Weigh 4N purity Bi2Te3 powder and Te powder in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum of 0.01 Pa, and melt at 620°C for 2 hours. Maintain a solidification rate of 0.05 K / s, cool to room temperature, crush the product to 200 mesh, and then place it into a mold. Isostatically press at 200 MPa for 20 minutes to obtain a green body with a diameter of 24 mm and a thickness of 4 mm. Place the green body in a vacuum sintering furnace, increase the temperature to 450°C at a rate of 5°C / min, hold at this temperature for 2 hours, and then cool it to room temperature with the furnace.

[0048] 2) Preparation of the evaporation body: A nickel-chromium alloy (chromium content 21 wt%) seamless tube with a diameter of 25 mm, an aspect ratio of 8:1, and a thickness of 0.1 mm was selected. A 3 μm thick Ti-Al2O3 coating was deposited on the inside of the seamless tube. Six evenly distributed circular holes were formed by laser drilling 20 mm from one end of the seamless tube, with a distance of 2 mm between adjacent holes.

[0049] 3) Using Aremco Ceramabond 571, the prepared evaporation source was fixed to the end of the chamber away from the circular hole in a manner such that the surface was perpendicular to the length of the evaporation body. The source was cured at 250°C for 30 min. The ends were then shrunk using a spinning machine with a compression of 4% per pass. The shrunk ends were then flattened to form electrodes. The flattening was performed in two stages: first, maintaining a pressure of 50 MPa for 20 s, and then impact loading was applied three times at 100 MPa with a pulse width of 0.5 s and a frequency of 2 Hz.

[0050] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film, wherein the substrate 5 was close to the circular hole and parallel to the tube, with a distance of 2cm from the tube. During the evaporation process, the operating temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.1°C. The evaporation film formation rate was relatively stable. The film thickness uniformity deviation was measured to be ≤1.4%. The product was relatively stable and the film formation speed was fast. After continuously coating 500 pieces of film, the evaporation device was still able to work stably. Figure 4 The SEM image shows that the film is composed of evenly distributed nanoparticles. Most of these nanoparticles are hexagonal flake structures with a particle size of about 50 nm, and the grain edges are clearly visible. Combined with XPS measurement calculations, it is shown that the Bi:Te atomic ratio in the product is 2:3.

[0051] Example 4

[0052] In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in two rows along the length direction of the seamless tube, and the circular holes have different sizes. The schematic diagram of the device is shown in FIG. Figure 5 , wherein the diameter of the large circular hole is 0.4 mm and the diameter of the small circular hole is 0.08 mm. The preparation method of the evaporation device is as follows:

[0053] 1) Preparation of the evaporation source: Weigh 4N purity Bi2Te3 powder and Te powder in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum of 0.01 Pa, and melt at 620°C for 2 h. Maintain a solidification rate of 0.05 K / s, cool to room temperature, crush the product to 200 mesh, and then place it into a mold. Isostatically press at 200 MPa for 20 min to prepare two green bodies with a diameter of 24 mm and a thickness of 4 mm. Place the green bodies in a vacuum sintering furnace, increase the temperature to 450°C at a rate of 5°C / min, hold at this temperature for 2 h, and then cool to room temperature with the furnace.

[0054] 2) Preparation of the deposition body: A nickel-chromium alloy (chromium content 22 wt%) seamless tube with a diameter of 25 mm, an aspect ratio of 8:1, and a thickness of 0.1 mm was selected. A 3 μm thick Ti-Al2O3 coating was deposited on the inside of the seamless tube. Six circular holes were evenly distributed in the middle of the seamless tube using laser drilling, with a distance of 2 mm between adjacent holes.

[0055] 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at both ends of the chamber so that the surface of the evaporation source is perpendicular to the length direction of the evaporation body. Curing at 250°C for 30 minutes, and using a spinning machine to shrink the ends, with a compression amount of 4% per pass. The shrinked ends are flattened to form electrodes. The flattening is carried out in two stages: first, maintaining the pressure at 50 MPa for 20 seconds, and then impact loading at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz for three times.

[0056] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.4°C. The evaporation film formation rate was relatively stable, and the film thickness uniformity deviation was measured to be ≤1%. The product was relatively stable, and the evaporation device was still able to work stably after continuous coating of 1,500 pieces.

[0057] Comparative Example 1

[0058] A bismuth telluride film evaporation device is disclosed, wherein the evaporation body is provided with two circular holes distributed in three rows along the length of a seamless tube, and the circular holes have a diameter of 1.5 mm. The evaporation device is obtained using the preparation method of Example 4, wherein no Ti-Al2O3 coating is deposited inside the seamless tube. A 2cm×2cm bismuth telluride film is prepared using the evaporation device. During the evaporation process, the maximum operating temperature change in the chamber of the device monitored by an infrared thermal imager is 2°C. The evaporation film forming rate is relatively stable. The measured film thickness uniformity deviation is 4.3%. The coating product is stable in the early stage, but some coating falls off after 1000 pieces are continuously coated.

[0059] Comparative Example 2

[0060] A bismuth telluride film evaporation apparatus is described. The preparation method is primarily the same as that of Example 1, except that the circular evaporation holes on the evaporation body are replaced with 10 mm long x 2 mm wide slits. The evaporation source is 4N Bi2Te3 powder placed in a quartz evaporation boat. A 2 cm x 2 cm bismuth telluride film was prepared using this evaporation apparatus. During the deposition process, infrared thermal imaging monitoring revealed a maximum temperature fluctuation of 5°C within the chamber, and the deposition rate was relatively stable. The film thickness uniformity was measured to have a deviation of approximately 5.9%. While the composition of the first few batches was stable, subsequent bismuth telluride films became less stable, with the appearance of impurities such as oxygen and carbon.

[0061] The above is a detailed description of a thermal evaporation device with a controllable evaporation rate for evaporating bismuth telluride films. The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention cannot be considered to be limited to these descriptions. For those skilled in the art of the present invention, its architecture can be flexible and varied without departing from the concept of the present invention, and a series of products can be derived. Simply making a few simple deductions or substitutions should be considered to fall within the scope of patent protection of the present invention as determined by the submitted claims.

Claims

1. A method for preparing a thermal evaporation device for evaporating bismuth telluride film, characterized in that: The following steps are involved: 1) Preparation of evaporation source: Weigh 4N purity Bi2Te3 powder and Te powder in a mass ratio of 99:1, mix the two, place in a vacuum melting furnace, maintain a vacuum of 0.01Pa, and melt at 620℃ for 2h. Maintain a solidification rate of 0.05K / s, cool to room temperature, crush the product to 200 mesh, and then place it into a mold. Isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm. Place it in a vacuum sintering furnace, increase the temperature to 450℃ at 5℃ / min, hold it for 2h, and then cool it to room temperature with the furnace. 2) Preparing a deposition body: Selecting a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1 to 10:1, and a thickness of 0.05 to 0.5 mm, depositing a Ti-Al2O3 coating with a thickness of 2 to 5 μm inside the seamless tube, forming a cavity inside the nickel-chromium alloy seamless tube, and using laser drilling to form 2 to 10 evenly distributed circular holes 20 mm from one end of the seamless tube, with a distance between adjacent circular holes of 0.5 to 2 mm. The circular holes have different diameters, with a small hole diameter of 0.02 mm to 0.1 mm and a large hole diameter of 0.2 mm to 0.5 mm; 3) Use high-temperature ceramic glue to fix the evaporation source to the end of the chamber away from the circular hole, cure it at 250°C for 30 minutes, use a spinning machine to shrink the ends and flatten the ends to form an integrated electrode; The thermal evaporation device can directly prepare a bismuth telluride thin film by thermal evaporation without vacuum conditions.

2. The method for preparing a thermal evaporation device according to claim 1, wherein: There are 6 circular holes distributed in three rows along the length direction of the seamless pipe, and the distance between two adjacent circular holes is 1 mm.

3. The method for preparing a thermal evaporation device according to claim 2, wherein: The large hole diameter of the circular hole is 0.5 mm, and the small hole diameter is 0.02 mm.

4. The method for preparing a thermal evaporation device according to claim 1, wherein: There are 6 circular holes distributed in two rows along the length direction of the seamless pipe, and the distance between two adjacent circular holes is 2 mm.

5. The method for preparing a thermal evaporation device according to claim 4, wherein: The large hole diameter of the circular hole is 0.4 mm, and the small hole diameter is 0.08 mm.

6. The method for preparing a thermal evaporation device according to claim 1, wherein: The compression amount of each pass during the shrinking is 3% to 5%. The flattening process is specifically carried out in two stages: first, maintaining the pressure at 50 MPa for 20 seconds, and then impact loading 3 times at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz.

7. A thermal evaporation device prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises an evaporation body made of a conductive material, an evaporation source and electrodes located at both ends of the evaporation body. A chamber is provided inside the evaporation body, the evaporation source is fixed at one end of the chamber, and 2 to 10 circular holes are evenly distributed on the end of the evaporation body away from the evaporation source. The distance between adjacent circular holes is 0.5 to 2 mm, and the diameters of the circular holes are different, wherein the small and medium apertures of the circular holes are 0.02 mm to 0.1 mm, and the large aperture is 0.2 mm to 0.5 mm. The evaporation body and the electrodes are integrally formed, and the evaporation source is Bi2Te3-1wt%Te.

8. The thermal evaporation device according to claim 7, characterized in that The evaporation body is made of a seamless tube made of nickel-chromium alloy, and the electrode is made by integrally forming the two ends of the seamless tube through shrinking and flattening.

9. The thermal evaporation device according to claim 7, characterized in that The chromium content of the nickel-chromium alloy is 20wt%-22wt%, the diameter of the seamless pipe is 25cm, the pipe wall thickness is 0.05-0.5mm, and the aspect ratio is 5:1-10:

1.

10. The thermal evaporation device according to claim 7, characterized in that The cavity surface of the evaporation body is provided with a Ti-Al2O3 coating, and the coating thickness is 2-5 μm.

11. The thermal evaporation device according to claim 7, characterized in that The distance between adjacent circular holes in the circular holes is 0.5-2 mm.

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